Generally, a wireless communication system encodes and modulates an original signal, and transmits the encoded and modulated signal. Such a wireless communication system uses a method of dividing a signal into different phase components and transmitting the phase components, or a method of dividing a signal into magnitude information and phase information and transmitting the magnitude information and the phase information.
A transmitter which divides a signal for transmission into the phase information and the magnitude information to transmit it is called a polar transmitter. When the polar transmitter transmits a signal, it does not divide the signal into an in-phase component, which is an I channel component, and a quadrature-phase component, which is a Q channel component and the signal is divided into the phase information and the magnitude information to be transmitted.
In the polar transmitter, a phase signal component is applied to a power amplifier as a signal which always has a predetermined magnitude through a phase modulator and a magnitude signal component is configured for a final Radio Frequency (RF) output to be a complex transmission signal by varying the power supply voltage of the power amplifier.
The general configuration and operation of the polar transmitter will be described with reference to FIG. 1.
FIG. 1 is a block diagram of a general polar transmitter.
Referring to FIG. 1, the polar transmitter includes a modulator 101, a digital signal processor 102, a phase modulator 103, a digital amplifier 104, and an antenna 105.
The modulator 101 receives data from an upper layer. In this way, the data provided to the modulator 101 is provided together with physical channel configuration information for the transmission of data from the upper layer. At this point, the modulator 101 modulates the received data.
When the modulator 101 modulates the data for transmission, the data are modulated according to the physical channel configuration information provided from the upper layer. Output data which are modulated by modulating in this way are illustrated as I(t) and Q(t) in FIG. 1. The signals I(t) and Q(t), which are complex digital signals outputted from the modulator 101, are inputted to the digital signal processor 102. Then, the digital signal processor 102 separates a phase information signal (θ) and a magnitude information signal from the input complex transmission data, and outputs the separated signals.
The phase information signal (θ) which is extracted and outputted by the digital signal processor 102 is inputted to the phase modulator 103, and the magnitude information signal is processed in a predetermined method and is inputted as a signal for the control of the digital amplifier 104. The phase modulator 103 outputs the phase-modulated RF signal by using the input phase information signal (θ). Herein, the phase modulator 103 may be implemented with a digital oscillator using a digital phase locked loop, and consequently outputs a phase-modulated wireless signal according to the input phase information signal (θ).
As another example, the phase modulator 103 may be implemented with a complex wireless modulator. In this way, in a case where the phase modulator 103 is implemented with the complex wireless modulator, the digital signal processor 102 must calculate and output a sine value and a cosine value. Therefore, the phase modulator 103 implemented with the complex wireless modulator generates and outputs a phase-modulated wireless signal by using an input sine value and an input cosine value.
The magnitude information signal extracted from the digital signal processor 102 may apply a Direct Current (DC) power supply voltage to the digital amplifier 104 through a rectifier (not shown in FIG. 1). At this point, the magnitude information signal extracted from the digital signal processor 102 may be a pulse type of an output signal through a Delta Sigma Modulator (DSM) or a Pulse Width Modulator (PWM) (not shown in FIG. 1), and a pulse width is determined according to the magnitude of a signal. The signal of pulse type is applied to the digital amplifier 104. The digital amplifier 104 performs switching onto the signal outputted from the phase modulator 103 based on a pulse-type control signal obtained in the DSM or PWM from magnitude information.
That is, the control signal of the pulse type outputted from DSM or PWM determines the amplification degree of the digital amplifier 104. The digital amplifier 104 can obtain a final output of the multiplication type of the phase-modulated RF signal and the magnitude information signal via a series of the processes. The signal, which is obtained from the digital amplifier 104 as the final output, passes through a band-pass filter (not shown in FIG. 1) and thereafter is finally radiated through the antenna 105.
As described above, the polar transmitter divides the signal for transmission into the phase signal component (θ) and the magnitude signal component. The magnitude signal component may go through one of the two methods as described above.
The first method is to apply the magnitude signal component to the digital amplifier 104 as a DC voltage by using a rectifier. However, in a case where the magnitude information is applied to the digital amplifier 104 as the DC voltage by using the rectifier, it is difficult to increase the switching speed of the rectifier when the bandwidth of the magnitude information is broadband, and efficiency is considerably decreased.
The second method is to use a delta sigma modulation scheme or a pulse width modulation scheme for transmitting the magnitude signal component. In the two schemes, the sampling speed of a signal must be implemented at very high speed in a digital domain for suppressing the increase of a noise or a spurious signal. Moreover, in a case where the magnitude of a transmitted signal is variable, the performance of DSM or PWM is considerably deteriorated in a system requiring the control of a transmission power.